1. Field of the Invention
The invention is related to a low noise amplifier (LNA) which utilizes an AC coupling technique that can internally bias the electrostatic discharge (ESD) protection diodes in such a way as to provide effective low noise amplification. The invention can also be utilized in power amplifiers to eliminate the need for external biasing.
2. Description of the Related Art
An amplifier is a device or circuit which produces an electrical output that is a function of the corresponding input parameter while increasing the magnitude of the input signal by means of energy drawn from an external source. This process, however, invariably introduces some noise and distortion into the signal. Low noise amplifiers are a special type of amplifier used in communication systems to amplify very weak signals captured by an antenna.
Conventional low noise amplifiers traditionally use an on-chip AC coupling capacitor to couple an incoming radio frequency signal (RF) without affecting bias. On-chip AC coupling capacitors are known to be used between input ESD diodes and a bias resistor. AC coupling serves to remove the static DC components from the input signal to the amplifier, leaving only the components of the signal that varies with time. Conventional placement of the AC coupling capacitor biases the input at zero volts unless external biasing is used.
It is an object of the present invention to provide a low noise amplifier using an AC coupling technique which can internally bias diodes and provide effective low noise amplification. The present invention can reduce capacitance of the ESD diodes and improve the noise figure of the low noise amplifier. The present invention can also be used to eliminate the need for external biasing of the ESD diodes in power amplifiers.